Command Line Interface(CLI)

What is CLI ?

CLI stands for Command Line Interface. CLI is a text-based interface that allows users to interact with a computer's operating system by entering commands.

Basic CLI commands in linux

cd command

cd means change directory. You invoke it specifying a folder to move into. You can specify a folder name, or an entire path.

Example:

mkdir hello
cd hello  # now your in the hello folder

You can use the .. special path to indicate the parent folder:

cd .. #back to the home folder

There is another special path indicator which is ., and indicates the current folder.

mkdir command

mkdir means make directory. mkdir command is used to create a folders.

mkdir fruits # fruits folder is created

You can create multiple folders with one command:

mkdir dogs cars

rmdir command

rmdir means remove directory. rmdir command is used to delete a folders.

mkdir fruits
rmdir fruits # deleting fruits folder

You can also delete multiple folders at once:

mkdir fruits cars
rmdir fruits cars

The folder you delete must be empty.

To delete folders with files in them, we will use rm command which deletes files and folders, using the -rf option:

rm -rf fruits cars

touch command

touch is used to create an empty file.

touch hello # creating empty file with name hello

pwd command

pwd means present working directory. It will print the current folder path.

pwd # print current folder path

ls command

ls command is used to list all the files inside folder.

ls

ls accepts a lot of options. One of my favorite combinations is -al. Try it:

ls -al # list all hidden and long term files

mv command

mv means move, it is used to moves files and directories from one directory to another or renames a files and folders.

touch test
mv pear new_pear

The pear file is now moved to new_pear. This is how you rename files and folders.

cp command

You can copy a file using the cp command:

touch test
cp apple another_apple

To copy folders you need to add the -r option to recursively copy the whole folder contents:

mkdir fruits
cp -r fruits cars

cat command

cat command on linux concatenates files together, cat can also add content to a file.

cat prints a file's content to the standard output:

cat file

You can print the content of multiple files:

cat file1 file2

and using the output redirection operator > you can concatenate the content of multiple files into a new file:

cat file1 file2 > file3

man command

man stands for manual, It is used to display the user manual of any command that we can run on the terminal.

man ls

echo command

echo command prints to the output the argument passed to it.

echo "hello"

will print hello to the terminal.

We can append the output to a file:

echo "hello" >> output.txt

open command

The open command lets you open a file using this syntax:

open test # open the test file

I use it all the time to open the current directory:

open .

nano command

nano is a beginner friendly editor.

Run it using nano <filename>.

You can directly type characters into the file without worrying about modes.

You can quit without editing using ctrl-X. If you edited the file buffer, the editor will ask you for confirmation and you can save the edits, or discard them.

The help at the bottom shows you the keyboard commands that let you work with the file:

chmod command

chmod stands for change mode, it is used to we can set 3 permissions: read, write, and execute.

The first letter indicates the type of file:

• - means it's a normal file

• d means it's a directory

• l means it's a link

Then you have 3 sets of values:

• The first set represents the permissions of the owner of the file

• The second set represents the permissions of the members of the group the file is associated to

• The third set represents the permissions of the everyone else

  chmod can be used in 2 ways. The first is using symbolic arguments, the second is using numeric arguments.

  1. symbolic argumnts:

  You type chmod followed by a space, and a letter:

  • a stands for all

  • u stands for user

  • g stands for group

  • o stands for others

      chmod a+r filename #everyone can now read
      chmod a+rw filename #everyone can now read and write
      chmod o-rwx filename #others (not the owner, not in the same group of the file) cannot read, write or execute the file
    

    2. numeric arguments:

This gives us 4 combinations:

• 0 no permissions

• 1 can execute

• 2 can write

• 3 can write, execute

• 4 can read

• 5 can read, execute

• 6 can read, write

• 7 can read, write and execute

We use them in pairs of 3, to set the permissions of all the 3 groups altogether:

        chmod 777 filename 
        chmod 755 filename 
        chmod 644 filename